Industrial mass production involves the pereformance of a large number of constantly repetitive assembly operations, for example tightening screws or nuts, by means of manual or motor-driven tools, in which respect an important consideration is that certain assembly parameters, for example the torque and/or the angle of rotation with or through which a screw or nut is tightened, coincide with predetermined reference values, within tolerance limits which are also predeterminable.
In the description of the present invention as set out hereinafter, consideraton is given only to assembly operations which are identical in regard to the purely external procedure involved, that is to say, which can always be carried out with one and the same kind of tool; however those assembly operations are referred to as being different from each other when the reference values in respect of one or more of the relevant assembly parameters and/or the tolerance limits within which those reference values have to be attained are different from each other. If for example one screw is to be tightened with a torque of 1 mkg.+-.10%, another screw is to be tightened with a torque of 1.5 mkg.+-.10% and a third screw is to be tightened with a torque of 1.5 mkg.+-.5%, then in the present context those situations involve three assembly operations which are different from each other, although they can be carried out with one and the same screw driving tool.
Tools which are referred to as `intelligent` tools are known, which on the one hand can be controlled to produce a presettable reference value in respect of at least one assembly parameter, wherein said presettable reference value can be a different one for each individual assembly operation, and which on the other hand include sensors for detecting the actual value which is actually attained, in respect of the at least one assembly parameter, and for converting that actual value into a corresponding actual value signal. Thus for example an `intelligent` screw driver or nut wrench or key may be of such a design that it automatically terminates the operation of tightening the screw or the nut respectively, when a predeterminable reference torque value is achieved. In that connection the value or the magnitude of the reference torque is variable and is preset from a control unit to which the tool is connected by means of a cable or by a wireless connecting means. After each assembly operation has been carried out, the actual value as detected by the sensors is transmitted to the control unit which checks whether it coincides with the preset reference value, within the associated tolerance limits which can also be preset. If the reference value and the actual value coincide within the tolerance limits, the assembly operation is deemed to be `good` and the workpiece is released for the next assembly operation or assembly step. If one of the reference values is not attained within the preset tolerance limits, the workpiece is generally removed from the production line and passed to an adjustment station.
It is quite possible for an `intelligent` tool of the above-indicated kind to be used to carry out in succession a multiplicity of different assembly operations, that is to say assembly operations in regard to which, in the most extreme situation, different reference values and/or different tolerance limits are preset on each occasion in respect of one or more assembly parameters. It will be appreciated that a necessary condition in that respect is that the various assembly operations are always carried out in the same sequence, once it has been preset, as the control unit calls up the reference values and/or tolerance limits for each assembly operation, in accordance with a set program. The operator of such a tool must know and precisely observe the sequence which is set down by the program, because otherwise assembly errors occur, which moreover cannot be recognised by the control unit as the control unit does not in fact have any information showing that the wrong reference value was preset. In such a situation, the control unit would only find that the actual values attained were coincident with the preset reference values within the preset tolerance limits, and would incorrectly identify as `good`, the assembly operation or operations in question.
It frequently happens that a production line involves the use of a number of identical or similar tools which however have to carry out assembly operations which are generally different in the above-indicated sense. If the control units of those `intelligent` tools are combined together to form a central control station, that central control station must generally preset different reference values for the various tools and must compare the actual values supplied by the various tools with the respectively correct reference values and/or monitor the attainment of different tolerance limits. As long as each of the tools is always used for the same assembly operation or for the same sequence of assembly operations, as is conventional practice in accordance wtih the state of the art, no problems arise in that connection because a predeterminable reference value or set of reference values and predetermined tolerance limits or a predeterminable sequence of such reference values and tolerance limits can be associated with each tool in a clear and uniform manner. Irrespective of whether a plurality of control units are combined together to provide a central control station or whether each tool is connected or equipped with its own individual control unit, in such a control and monitoring arrangement which is in accordance with the state of the art, a tool can only ever be used for one and the same assembly operation or one and the same sequence of assembly operations, which sequence must be precisely observed, if the operator is not to be in a position of constantly changing the reference value or values and/or the tolerance limits in respect of the assembly parameters, which is something that cannot be done in the practical situation of industrial mass production.
On the other hand however it is desirable to be able to use one and the same `intelligent` tool for various assembly operations in any desired sequence; that is necessary for example in regard to adjustment operations on the workpieces which are removed from the production line at various locations for the reason that the actual values of the respective assembly operation do not coincide with the applicable reference values, within the associated tolerance limits. Hitherto only simple tools which do not permit monitoring of the assembly parameters produced therewith have been used for such constantly varying adjustment assembly operations.
In comparison with that art, it is an objective of the present invention to provide a control and monitoring arrangement for tools which makes possible to carry out various assembly operations in any sequence by means of an `intelligent` tool, without the operator being required in that connection to make any alterations at the monitoring system or to introduce fresh data.